The invention relates to an arrangement and a method for mounting a power semiconductor module onto a cooling element. In one embodiment, the power semiconductor module has a module housing, in which connection contacts are led out laterally from the module housing parallel to the underside of the module housing.
A customary construction of a power semiconductor module and the arrangement thereof on a heat sink are illustrated in FIGS. 1 to 4. Power semiconductor components 5, 6, 7, 8, 9, 10, 11, 12 are situated on a substrate 2, which can be embodied as a ceramic substrate, leadframe, IMS (Insulated Metal Substrate). The power semiconductor components 5 to 12 are normally soldered onto the substrate. The external wiring of the substrate 2 is effected using a multiplicity of connection contacts 15, wherein the connection contacts 15 are typically fitted to the longitudinal edges of the substrate 2 using a leadframe 1.
It is also possible, instead of a substrate 2 with power semiconductor components 5 to 12, to connect the power semiconductor components directly to the leadframe. The leadframe 1 contains, alongside the connection contacts 15 that occupy all the connections of the substrate upon application of the leadframe, in addition peripheral webs 20, 21 that mechanically stabilize the connection contacts 15. The electrical contacts of the substrate 2 are peripherally fixed with the connection contacts 15 of the leadframe 1, wherein this fixing can be effected by soldering, welding, adhesive bonding or other connecting techniques.
A substrate 2 provided with power semiconductor components 5 to 7, which substrate forms a leadframe 1 using the connection contacts 15, is illustrated without a housing in FIG. 2. The peripheral webs 20, 21 of the leadframe 1 have been removed in this case.
In order to encapsulate the power semiconductor module, the leadframe 1 is encapsulated with plastic by injection molding, as illustrated in FIG. 3. In the process of encapsulation by injection molding, the mold parting of the injection mold always seals above the peripheral web 20 of the leadframe 1, which simultaneously orients and stabilizes the individual contacts 15 during the encapsulation by injection molding. In order to seal the injection mold, after the injection mold has been brought together (for directions of movement, see arrows in FIG. 3), the mold parting must always be brought to a defined area (dashed line in FIG. 3) corresponding to the inner part of the peripheral webs (20).
After the encapsulation by injection molding, superfluous connection contacts 15 that are not required according to the circuit layout of the substrate 2 and the peripheral webs 20, 21 are removed. For cost reasons, the removal can usually be effected using stamping. The leadframe 1 illustrated in FIG. 2 with a module housing 40 applied around it by injection molding is illustrated in FIG. 4. On account of the costs for the plastic used of the module housing 40, the housings 40 are made as flat as possible.
The power semiconductor module 3 finished in construction with a module housing 40 is mounted by the underside 50 onto a heat sink or cooling element 4 (FIG. 4), wherein the mounting is usually effected by screwing or clamping. The heat sink 4 serves for dissipating the power loss which arises in the power semiconductor components 5 to 12 and which occurs in the form of heat. As illustrated in FIG. 5, the module housing 40 bears by its module housing underside 50 on the heat sink 4 areally and without any gaps for an effective heat dissipation or a low heat transfer resistance and hence reliable operation of the power semiconductor module 3.
The connection contacts 15 of the power semiconductor module 3 are led out laterally from the module housing 40 parallel to the underside 50 of the module housing 40. For an external connection, the connection contacts 15 run outside the module housing in a manner leading away from the heat sink at an angle of greater than 180° with respect to the underside 50 of the module housing 40. Due to the arrangement of the connection contacts 15 with respect to the heat sink 4, which is grounded, the connection contacts 15 are at only a small distance from the heat sink 4 in that region in which the connection contacts are arranged outside the module housing 40 parallel to the underside 50 of the module housing 40.
The small distance between the connection contacts 15 and the heat sink 4, which can be merely a few millimeters, sometimes even less than 1 mm, is manifested in the form of a small air clearance 45 and a small creepage path 46, that is to say an excessively small insulation clearance. Therefore, power semiconductor modules 3 which—as illustrated in FIG. 5—are arranged on a heat sink can usually be used only for reverse voltages in the range up to 600 V. At higher voltages, in particular in the case of the widespread 1200 V class, complicated additional measures in the application construction have to be taken for the use of the power semiconductor modules 3.
Additional measures are necessary in order to upgrade the modules for higher voltage classes: alongside milled-out portions in the heat sink 4, in the case of modules that are not insulated with respect to the heat sink—usually when a pure leadframe is used as component carrier—additional insulator films are customary, although they impair the thermal properties of the arrangement of power semiconductor module and heat sink 4. The insulator films are always situated between the power semiconductor module underside 50 and the heat sink 4, wherein the films having a thickness of a few tenths of a millimeter usually include Kapton, polyimide or similar electrically insulating materials. Owing to these additional outlays, present-day power semiconductor modules which are encapsulated with plastic by injection molding and which are arranged on a heat sink are not used very widely in application with reverse voltages in the range up to 1200 V.
For these and other reasons, there is a need for the present invention.